This invention generally relates to locking mechanisms, and more specifically to a pick-proof lock cylinder and key therefor.
Most lock mechanisms in use include a housing having a generally cylindrical bore therethrough in which is mounted a revolving cylinder or tumbler. A plurality of biased pins or plungers are provided which cooperate with the housing and the revolving cylinder to enable or inhibit the rotation of the tumbler, the plungers or pins being arranged to detect a suitably coded key which actuates one or more of these plungers or pins. With most commonly used constructions, the revolving cylinder or tumbler is mounted in a through bore of the housing, and the keyhole which accepts the key extends substantially through the revolving cylinder. The pins or plungers are typically arranged along the axis of the tumbler and engage the key as the same is moved into the keyhole.
A problem which exists with most lock cylinders in use today is that the above-described constructions make it possible for the locks to be violated by picking or partially destroying the same. Picking of such locks has been facilitated by the fact that the plungers or pins are arranged in line with the keyhole and, therefore, are readily accessible to one who is skilled in picking such locks, Other locks have the decoding pins or plungers situated proximate to the keyhole or to the keyhole opening so that their operation may be destroyed by drilling into one or another portion of the revolving cylinders. Most typically, revolving cylinders of this type may be made inoperative by simply drilling a hole along the axis of the keyhole and thereby destroying the decoding means or the pins and plungers which are arranged to sense the key.
As suggested above, most revolving cylinders of commonly used locks extend substantially the entire length of the housing and, therefore, are exposed and accessible at the opening of the keyhole. This permits tampering with the revolving cylinder and the picking thereof.
Various attempts have been made to overcome the above-mentioned problems and to minimize the risk of having a lock picked. Some early attempts at overcoming the problem are exemplified in U.S. Pat. Nos. 866,697 and 888,478. In the first mentioned patent, a key was used which had a bifurcated resilient member at one end thereof which was adapted to engage a suitable actuating mechanism within the lock. The portions making up the bifurcated end of the key were slightly spaced from the axis of the key. However, this lock did not utilize a cylinder of the type commonly used today and did not use pins or plungers. Instead, the lock of this reference utilized a sliding latch arrangement which would not provide much pick-proof protection. The bifurcated end of the key was initially compressed by a channel of reduced diameter which was in turn provided with a pair of slots internally of the lock which permitted the bifurcated end to expand when brought into registry with the slots. At such time, the bifurcated end could engage and actuate the latch mechanism. The second patent was also for a lock but utilized a key which was in actuality a double key, one portion having a straight shank and the other portion having a curved shank, with both portions being pivotally connected to each other. Before the latch mechanism of this lock could be actuated, it was necessary to insert the key in such a manner so that both straight and curved shank portions engaged respective or cooperating elements within the lock.
Further attempts have been made to produce a pick-proof lock. These have included locks which use a key having a pivoted free end which is adapted to turn or rotate a predetermined angular distance upon full insertion of the key into the lock to engage an element which would not otherwise be engageable by a straight shank. For example, in U.S. Pat. No. 1,596,336, a lock is disclosed which uses a key having a pivoted end member which is initially aligned with the shank of the key in one position thereof. However, when the key is turned approximately 180.degree., the pivoted end portion moves, due to gravity, to a position which permits the same to engage a latch. Further rotation of the key causes the latch to move. In order to provide somewhat more control over the action of the key, and more particularly over the pivoted free end thereof, further constructions have been proposed wherein the position of the pivotally mounted free end may be controlled at the exposed end of the key or in the region of the gripping portion thereof. Such constructions are disclosed in U.S. Pat. Nos. 1,464,194 and 1,750,542. In all of these patents, however, the movement of the pivoted end towards the final or operative position only causes the pivoted portion to engage a latch or the like and could not, in and of itself, be utilized with the more modern and more complex locks which are in use today.
Other locks which are known in the prior art include a key which has a pivotally mounted finger thereon, the finger itself being provided with a cam surface which engages an abutment upon insertion of the key into the cylinder to cause the finger to be deflected from its initial axially aligned position to one where the fingers may be approximately 90.degree. displaced from that initial position. In U.S. Pat. Nos. 1,274,313 and 2,296,029, these pivotally mounted fingers engage a latch mechanism in the pivoted or actuating position, while in U.S. Pat. No. 1,567,979, the finger engages a pair of spring loaded pins or plungers. However, the last described construction has the disadvantages above described since it includes a revolving cylinder exposed to the outside and, therefore accessible for tampering therewith. Additionally, the spring loaded pins or plungers are mounted substantially in line with the keyhole and, therefore, this invites for the lock to be violated by simply drilling through the keyhole.
As an examination of the abovementioned patents will reveal, most prior art key constructions which have utilized pivotally mounted end portions are generally for large and bulky locks and are impractical for most common consumer uses.